Light source and method of use



May 6, 1958 J. cs. KOOSMAN LIGHT SOURCE AND METHOD OF USE 2 Sheets-Sheet 1 Filed July 27. 1954 INVENTOR. JOSEPH G. KOOSMAN ATTORNEYS Miay 6, 1958 J. G. KOOSMAN 2,833,954

LIGHT SOURCE AND METHOD OF USE INVENTOR. JOSEPH G. KOOSMAN A TTORNEYS United States Patent LIGHT SOURCE AND METHOD OF USE Joseph G. Koosmau, Clifton, N. J., assignor to Alien B.

Du Mont Laboratories, Inc., Clifton, N. J., a corporation of Delaware Application July 27, 1954, Serial No. 446,015

9 Claims. Cl. 314-134 This invention comprises improvements in light sources with special reference to a light source which approximates a point source.

This invention also comprises a method of manufacturing color cathode ray tubes employing the light source of this invention.

There are many uses for light sources of limited size which produce illumination of high intensity. Many efforts have been made to provide sources of light which produce their illumination in great physical concentration so as to approximate a point source. Glass enclosed gaseous-discharge or incandescent sources, while intense, produce light which, in concentration, deviates Widely from a point source. In addition, this type of source has the disadvantage of causing blackening deposits on the interior surface of the glass enclosure.

Another disadvantage of these sources is that as a concomitant of intensity their life is greatly shortened.

Carbon arcs, while approaching the desired pinpoint requirement, have a ltuninescent flare which nullifies to some extent the desired pin-pointing condition. In addition, the negative rod-electrode of previously known carbon arcs often casts a disturbing shadow.

A primary object of this invention is to provide :a novel form of light source, specifically an electric are light which provides the brilliance of electric arcs but which is so constructed as to constrict or concentrate the lightemitting area of the arc to a very close approximation of a true point source.

Another object of this invention is to provide a novel and eflicient method employing the light source of this invention in the production of the fluorescent screen of a color cathode ray tube.

Other objects of this invention will be apparent from the following description of the embodiments thereof illustrated in the accompanying drawings.

In those drawings,

Figure l is a simplified broken view partly in crosssection of a complete color cathode ray tube in the manufacture of which the utility of the novel subject matter herein disclosed will be demonstrated;

Figure 2 is a simplified somewhat diagrammatic view of the light source of this invention showing its manner of use in the manufacture of color cathode ray tubes; and

Figure 3 is a View in perspective partly broken away illustrating a practical apparatus utilizing the principles diagrammatically illustrated in Figure 2.

Because of the importance of a point source of light in the manufacture of color cathode ray tubes the description of the point source of this invention is related to the manufacture of such tubes, but it will be understood that there are many other uses for this type of light source, both in the practical and scientific arts. As a background for a full appreciation. of the nature and utility of this invention a brief discussion will first be given of a type of color television cathode ray tube in the manufacture of which the light source of this invention has great utility. Such a tube is diagrammatically illustrated in Figure 1. This tube is generally indicated at 11 and consists of a glass envelope of enlarged crosssection having an integral tubular neck portion within which is mounted a plurality of electron guns, in this case three. Two of the three guns, that is, 12r and 12b, appear in elevation in Figure 1 it being understood that the third gun 12g cannot be seen as it lies behind the gun 12b. The enlarged end of the glass envelope is provided with a flange 18 which is sealed to the flange 19 forming an integral part of a glass face plate 13 having on its inner face 16 a layer 14 of fluorescent materials. A dome-shaped foraminous mask 17 which is preferably concentric with the curved faceplate 13 is supported within the glass envelope in any suitable manner. At the other end of the neck portion is the usual base with its terminal prongs. the neck is a deflection coil 24. Since no feature of the cathode ray tube forms a part of the invention herein disclosed and is only used for illustrative purposes, the

above generalized description of this tube is deemed adequate.

As will be explained later the fluorescent layer 14 is discontinuous and is made up of groups of elemental areas each consisting of dots or bodies of materials which fluoresce in different colors under electron excitation and more specifically consisting of three dots, one producing red, another blue and another a green light under excitation. This excitation is pr-oduced by the three corresponding electron guns 12r, 12b and 12g which are energized by suitable electric potential signals representative of the corresponding color characteristics of a scene to be reproduced. These guns produce the corresponding electron beams 21r, 21b and 21g which beams are bent by convergence fields to converge at a single small aperture 22 of the mask 17 at some instant in the scanning travel of those beams as is well understood in this art. A function of the mask 17 is to shade or mask the fluorescent layer 14 so that, for example, electrons from. the beam 211' can pass through the apertures of which aperture 21 is an example to strike only the red fluorescing material in the elemental areas associated respectively with said apertures. Similarly, electrons from the beam 211) strike the blue fluorescing material and electrons from the beam 21g strike the green fluorescing material. The elemental areas each comprising a dot of each of the three fluorescing colors are interspersed over the face of the plate 13 to provide the discontinuous layer 14 and are arranged in a regular pattern with respect to the apertures 22 to provide the shading or masking eifect mentioned above.

The electron beams 21r, 21b and 21g are deflected by means of a deflecting coil 24 as is Well understood, each beam is being deflected as if it originated from a single point. In the case of the electron beam 211' the apparent point of origin is indicated by the reference character 26r while the apparent points for the beams 21b and 21g are indicated as at 26b and 26g. As is known in this art no matter how the electron beams are deflected by the coil 24, they always appear to emanate from these three apparent points of origin.

One of the greatest diificulties in fabricating cathode ray tubes of this type is in the production of the fluorescent screen or layer 14. For this purpose the arc source of the invention herein disclosed is especially useful in a photographic process for depositing the fluorescent materials in the elemental areas referred to. As a general description, the following procedure is followed.

The inner surface 16 of the faceplate 13 prior to sealing its flange 19 to the flange 18 is coated with a mixture or slurry comprising a photosensitive material and a phosphor material of a type which fluoresces, for example, to

Patented.May 6, 8

Mounted on or positioned about produce green light. The coated faceplate 13 and the mask *17 are mounted 'inproper spaced relation "with -respect to each other and a point source of light which in space ,is located at the point corresponding to the point 26g. Light from the point source passes through the aperture inthe mask "17 and strikes'portions of'the photosensitive coating mixture on the 'faceplate 13. The exposed layer is then developed'so as to formsmall islands or dots of phosphor material on the surface of-faceplate 13. These dots are composed of the fiuorescent'material which, under electron excitation, gives off green light. As a result of the development all of the unexposed coating is removed. The process is-then repeated with a mixture of photosensitive material and aphosphor which fluoresces to produce blue light. The point light source is then mounted so as to "be located atthe apparent point of origin 26b. The exposed *coating'is again developed leaving dots of the *blue 'fiuorescing characteristics while the unexposed portions of this coating are removed. Since the light passed-through the apertures in*mask 17 from a different p'oint'of origin than in the first exposure, different areas of the inner face of the faceplate 13 were exposed and hence retain the dots of blue fluorescing material. The faceplate now has two sets of dots, one having green fluorescing characteristics and the other blue fluorescing characteristics. The second exposure and development of course does not adversely affect the dots of green fluorescing material because they are no longer light-sensitive due to development and further because they were shielded by the mask during the second exposure. As a result of these two steps approximately two-thirds of-the faceplate has been coated. The process is again repeated to produce the final set of dots of red fluorescing material, inthis case the point source of light being placed at the point of origin 26r. Thus by these successive steps and as determined by apertures 22 in the mask 17 a plurality of elemental areas each comprising three dots one of green fluorescent material, one of red fluorescent material, and

one of blue fluorescent material are produced. The net result is that the entire inner faceof the'faceplate 13 is covered with minute dots of'fluorescent material arranged in 'anorderly manner.

It will be understood by those skilled in this artthat after each exposure the processing of the coating results in the formation of insoluble dots. The unexposed portions of the coating are still soluble and so after each development the undeveloped portions are washed away leaving the glass plate clear thereat. Thus when the second coating is applied its exposure-will occur in areas adjacent to the previously exposed areas so that upon its development and washing a second set of permanent dots will be formed. Similarly a third and, in the case described, final set of dots will be formed. The final result will be a discontinuous coating of discrete dots whichcan be divided into elemental areas. In each of these elementalareas there are threepermanent dots, one containing a blue fiuorescing phosphor, another a green fluorescing phosphor, and the final dot containing a red fluorescing phosphor. Naturally it is within this invention to provide less than or more than three dots in each elemental area by the same procedure.

As is well understod the sets of 'phopshor dots determine the quality of the color picture produced by the tube and theymust be very precisely formed and positioned. Any deviation from the shapeas determined by the aperture 22 in the mask17 would impair the color purity; for thenelectrons'from any'onelgun would excite apart of a different color phosphor dot than is intended to be excited by that gun, resulting in color deterioration. As previously mentioned, the lightsource used in this process to the extent that it deviates from an ideal point source, would interfere with the proper formation and placement of the phosphor dots introducing an in herent color deteriorating factor into the tube structure.

From the above the utility of the invention now to be described will become apparent.

Refering to Figure 2, there is shown somewhat diagrammaticaly an arc type of light source having a close approximation to an ideal point source. At 29 is a carbon rod which is preferably in tubular form and is filled with a core 29' of suitable material of types well-known in the art and used because of their'ability to generate light of high intensity. Positioned in front of the rod 29 is a relatively heavy plate 28 likewiseof carbon having an outwardly flared aperture 30 positioned on the of the rod. At 31 is diagrammatically illustrateda suitable source of operating currenthaving its positive terminal connected to the rod 29 and its negative terminal connected to the plate 28. The included angle of the aperture 30 is such that all the light from the crater 32 reaches the mask 17 of the assembly which includes the faceplate 13 and the photosensitive coating on the face thereof representing one or the other of the coatings previously referred to.

When the arc is started by momentarily *touching the two electrodes 29 and 28 together and then separating them, the current travels from the positive car bon rod to a point on the inner periphery of the conical aperture 30. By proper design the arc maybe made extremely short and the luminescent -*fiare maybe masked :by-the negative electrode 28 'sothat efiectively apoint of source of light is achieved.

This arrangement produces many advantages heretoforeunattainable. First it provides a truepoint source without any luminescent gflare area such as is usually produced with a carbon'arc. The crater of *light is perfectly round and extremely bright, and at an appreciable distance has .allthe characteristics of a truepoint source of light. The brightnessyof this source'can be controlled by varying the current .supplied to'the electrode. Because of the high intensity of this source, in the process described the interval of exposure is relatively quite short. In the process herein described with the usual light sources an exposure of as much as minutesis' required which exposure period is reduced by'the light source of this invention to about 90 seconds; R of course follows since a point source is approximatedthat theiresultant phosphor dots are accurate copies of the aperture configuration in the mask 17 which, being circular as shown, ensures the production of circular dots.

Another advantage of this invention is that using cored carbon rods the core material can be varied so-that in association with theproper photosensitive materials;eflicient actinic responses can be secured. Becausethe electrode 28 is relatively massive it. has a long life in comparison with the usual rod electrodes-heretofore used, thereby reducing replacement and maintenance problems. In addition, the arc tends to strike at various points around the periphery of the aperture-so thatoxidation effects are distributedthereby promoting long-life of this electrode.

There is illustrated in Figure 3 in more detail a practical form of apparatus for employing the-lightsourceof this invention in the production of color cathode ray tubes. This device includes a suitable housing and support 37 having a faceplate 50 with a large circular aperture therethrough which is defined by a mounting plate 51 having a plurality of clamping devices 36 distributed around its face. These clamping devicesprovide a simple method of holding the faceplate13 in alignment with the aperture in the wall'50-by engagement with its rim 18 as illustrated in this figure.

The light source is mounted within the enclosure :37 in a special fixture by means of which it may be manipulated for the illustrative use herein described. Thus withinthe enclosure'is a suitable stand -on'which are mounted in suitable 'bearing members-twopaizsof flanged rollers 39, 40 and 41, 42. These rollers provide a rotatable support for a cylindrical cage consisting of a pair of end plates 52 and 53 rigidly interconnected by a series of axially extending rods 54. Slidably mounted on an opposite pair of these rods is a carriage consisting of a pair of members 58 interconnected by a tubular support 55 and provided with a knob operated adjusting mechanism 59 of any suitable and well-known construction to cause axial movement of the carriage. This adjustment could include a gear engaging a gear rack formed on the associated rod 54 or could consist of a friction wheel engaging the surface thereof. The tubular support 55 has a chuck 56 formed on the end which can be tightened and loosened by means of a knurled knob 57. This chuck can be of any suitable form and proportioned so that when tightened it will hold the carbon rod 29 in the end thereof.

The end plate 53 is provided with an opening 60 over which is mounted an aperture supporting plate 61 on which the plate electrode 28 is secured with its aperture aligned with the axis of the rod 29. The end plate 52 is provided with three peripherally positioned notches 46, 47 and 48 arranged to cooperate with a latching device 49 which could be a spring-controlled detent of wellknown construction. By means of this indexing mechanism the electrode supporting cage can be locked in the three desired positions.

It is to be particularly noted in connection with Figures 2 and 3 that the axis of the electrodes 28 and 29 is not on the axis of the curved face of the faceplate 13. The reason for this is that as the cage is rotated to any one of its three positions on the rollers 39 to 42 inclusive, the axis of the arc will rotate about the axis of the faceplate so that in each of its three positions the arc can take the corresponding positions of the apparent points of origin 26r, 26b and 26g. In other words, this is a specialized condition for the purposes of illustrative use.

The carriage assembly has the obvious purpose of permitting the starting of the arc and the axial positioning of the rod electrode 29 as it wears away in use.

From the above description it will be apparent that I have devised an extremely novel and useful form of light source the details of construction of which, as well as the manner of its use, can be varied to meet diiterent conditions as will be readily appreciated by those skilled in the art. I prefer therefore not to be limited to the disclosure but rather by the claims granted to me.

What is claimed is:

1. In an are light of the incandescent crater type, the combination comprising: a cathode comprising a plate having an aperture therethrough, said aperture having the configuration of a truncated cone; and an anode comprising a rod positioned in free air so that said incandescent crater at the end thereof is at the projected apex of said truncated cone whereby light from said crater passes through said aperture, while light from the arc itself or the fluorescent flare thereof is masked by the solid portion of the plate surrounding said aperture.

2. In the are light of claim 1, said rod electrode lying at right angles to the plane of said plate electrode.

3. In the combination of claim 2, said rod electrode lying on the axis of the aperture in said plate electrode.

4. In the combination of claim 3 said rod being of carbon.

5. In the combination of claim 3 said plate being of carbon.

6. In the combination of claim 4, said rod electrode being cored.

7. In the combination of claim 3, means for maintaining the position of said crater at said apex, said means comprising apparatus for longitudinally positioning the rod electrode with respect to the plate electrode.

8. An are light combination as disclosed comprising a rotatable cage, means for indexing said cage at any one of several angular positions, an are light electrode eccentrically mounted with respect to the axis of said cage, a carriage adjustable on said cage for supporting said electrode, and a second are light electrode having an aperture therethrough mounted on said carriage so that the axis of said aperture is on the axis of adjustment of said carriage.

9. An are light which produces substantially a point source of light, comprising: a cathode consisting of a plate having a frusto-conical aperture therethrough, said aperture having a major and a minor diameter; an anode electrode comprising a rod having a light-emitting crater at one end thereof, said are light structure being positioned in free air, said rod electrode being coaxial with said aperture, and said crater being in close proximity and substantially equal to said minor diameter, whereby the fluorescent flare of the arc is effectively masked.

References Cited in the file of this patent UNITED STATES PATENTS 1,216,696 John Feb. 20, 1917 1,323,304 Mauclaire Dec. 2, 1919 1,784,171 Bertling Dec. 9, 1930 1,900,578 Moore Mar. 7, 1933 1,949,276 Huffman Feb. 27, 1934 2,116,901 Knoll May 10, 1938 2,266,287 Thom Dec. 16, 1941 2,453,118 Buckingham et al. Nov. 9, 1948 2,609,484 Benard Sept. 2, 1952 2,625,734 Law Jan. 20, 1953 2,657,133 Weingarten Oct. 27, 1953 2,733,366 Grim et a1 Jan. 31, 1956 OTHER REFERENCES Sylvania Technologist, vol. VI, No. 3, July 1953, pages -63. 

